Rural Funds Group has bought the lion's share of a new water allocation on Queensland's Lower Fitzroy River, a deal that provides the vital ingredient for its ambitious plan to establish a $1.5 billion portfolio underpinned by macadamia orchards.

The country's largest listed farmland trust will pay $32.4 million for a 21,600 megalitre allocation sourced from the Rookwood Weir, which is being built 66 kilometres south-west of Rockhampton.